Joseph S. Wall Composition of Sorghum Plant Charles W ... · Composition of Sorghum Plant and Grain1 INTRODUCTION As cultivation of sorghum became widespread, different varieties

Joseph S. WallCharles W. Blessin

CHAPTER 4

Composition of Sorghum Plant

and Grain1

INTRODUCTION

As cultivation of sorghum became widespread, different varietieswere selected for specialized uses. Sweet sorghums were bred forthe sugar contained in their stems and for succulence for use as forages.Among varieties, the grain may differ in amount, color, size, and chemical composition. During plant development, changes in compositionoccur that are important in selecting the times of cropping for forageor other uses. 'When compared to other grain or forage crops, sorghumscontain distinctive components that offer advantages or may requirespecial consideration during utilization. Therefore an evaluation ofa range of compositions related to varieties and hybrids, conditionsof cultivation, and time of cropping is essential to select materials foroptimum specific uses as food, feed, or fiber. This chapter will discusssome factors which influence the composition of plants and grains ofvarious types of sorghums and will describe some of the characteristics of their constituent carbohydrates, proteins, lipids, pigments,minerals, enzymes, and other substances.

PROXLvlATE ANALYSIS

Proximate analysis of plant materials consists in determining themajor classes of chemical components, which include moisture, crudeprotein, crude fat, fiber, ash, and nitrogen-free extract. Protein inmany feed materials, including sorghum, is approximated by multiplyingthe Kjeldahl nitrogen analysis by the factor 6.2.5. Crude fat is measuredas diethyl ether or petroleum ether extractable material. Crude fiberrefers to combustible organic matter not solubilized by either hot dilutesulfuric acid or dilute sodium hydrOxide solutions. Ash is determinedby igniting samples until free of carbon. Nitrogen-free extract is thedifference between the sum of these constituents and the original drysample weight. Rapid, reproducible, uniform methods are publishedby the Association of Official Agricultural Chemists (1965) and by theAmerican Association of Cereal Chemists (1962). Proximate analysis

1 Contribution from the Northern Regional Research Laboratory, Peoria, Illinois... This is a laboratory of the Northern Utilization Research and Development Divi

sion, Agricultural Research Service, U.S. Dept. of Agr.

118

COMPOSITION OF SORGHUM PLANT AND GRAIN 119

provides a good initial impression of the relative nutritive value andutility of an agricultural commodity, and allows a basis of comparisonbetween different species, plant parts, and cultivation conditions. However, based on his studies, Van Soest (1967) cautions against usingproximate analysis data as the only criteria for feed value.

Proximate Analysis of Forage

Variations Due to Varieties and Hybrids.-The composition of hybridforage sorghums favors their use as fodder, silage, and other feedcomponents for ruminants in many areas where they provide betteryields than corn. Corn and sorghum forage compositions are fairlysimilar, although greater grain content in the corn forage accountsfor its slightly higher levels of crude protein and low"er contentsof crude fiber than sorghum forages (Table 4.1).

TABLE 4.1CHEMICAL AX,\LYSIS OF FORAGE SORGHUMS AXD CORX

Nitrogen-Dry Crude Crude Crude free

Matter, Protein, Fat, Fiber, Ash, Extract,C1 % C1 C1 C1 % ReferenceIe /0 Ie Ie

36.1 8.34 3.52 26.4 5.61 56.1

24.25 5.4 4.4 27.3 8.07 54.824.6 7.3 2.9 23.6 9.72 56.424.3 6.7 4.8 32.8 12.8

Forage

CornSorghum

AtlasFS-1AFS-22Brawlev

(sweetforage) 27.4 6.2 £.5 :W.6 7.6

1 Nordquist and Rumer," (1967).2 Garret and Worker (1905).

In general, the more grain that varieties of sorghum will yield, themore starch, lipid, and protein the entire plant will contain alongwith less fiber. In Table 4.1 are compared analyses of plants fromDeKalb FS-1A, a high-grain-yielding forage hybrid; FS-22, a lowgrain producer; and Atlas, an intermediate grain producer. Nordquistand Rumery (1967) found that FS-1A contains Significantly less fiberthan FS-22, whereas Atlas is intermediate in fiber content. Ramseyet al. (1961) noted that forage of RS 610, a short combine type ofhybrid grain sorghum, has only slightly less fiber (28 %) as comparedto tllat of Tracy, a s\veet sorghum (30%), but significantly more protein (11 versus 5% ).

Another factor that greatly influences the composition of sorghumforage is the relative amount of leaf and stalk in the plant since leaves

120 SORGHUM PRODUCTION AND l.JTILlZATION

are higher in crude protein and fat than stalk. Table 4.2 comparescomposition of plant parts of Atlas forage (Stallcup et al. 1964). Thurman et al. (1964) showed that the better leafage in new sorghum hybrids improves their protein content.

TIle ratio of leafage to stalk also influences the level of nuh'ients insudangr·ass. Gangstad (1964) found in a series of sudangrass varietiespositive correlation between leafiness and protein and fat content, andan inverse relationship between fiber and leaf content.

Effect of Development and Agronomic Factors.-The composition offorage sorghums has been determined at various stages of plant development to establish systems of crop management that give optimumyields of nutrients (Webster and Davies 1956; EHrich et al. 1964; Webster 1963; Bettini and Proto 1960). The gr'eatest yield of total forage

TABLE 4.'!CHEMICAL ANALYSIS OF FORAGE SORGHUMS HARVESTED FOR SILAGE

Dr~' Matter

Ether CruderJant, Protein, Extract Fiber, Ash,

Forage Material 07 C7 C7 C7 0;;,iO /0 Ie iC

AtlasWhole plant 100.0 5.7 1.9 '!3.6 4.7Leaves and sheath '!1. '! 7.7 3.1 29.9 8.2Stalks 55.1 3.0 0.8 26.1 3.9Head 23.7 10.0 3.5 12.2 3.4

Source: Stallcup ct al. (1964).

?\itrogenfree

Extract,C7/0

64.151. 166 270.9

from Atlas sorghum comes during the hard dough stage of grain development. Ash ranges from 8 to 11 % in young plants (30 in.), butafter heading decreases to 4 to 5%. Ether exh'act will vary between1 and 2%. In early stages of growth, protein accounts for 12 to 18%of dry weight, but drops to 5 to 8% as the plant reaches maturity.The decline in protein is most marked in tlle leaves and stem. Proteincontent of heads initially increases rapidly but levels off (EHrich et al.1964). Maximum protein yield does not coincide with maximumforage yield, but occurs earlier at the soft dough stage of grain. Fibercontent decreases from a level of around 35 % in the young plant toa minimum, 24%, during heading, and then rises slightly as maturityis reached. The nitrogen-free extract rises from a low value of 45%to about 60% when tlle grain is formed.

Degree of plant maturity also affects the quality and compositionof sudangrass and sorghum-sudangrass hybrids for use in grazing or

COMPOSITION OF SORGHUM PLANT AND GR.·UN 121

hay. Stallcup et al. (1964) determined proximate analysis of PiperSudan grass forage cut at different stages of growth. There is a steadydecline in protein content, 17% at 18- to 24-in. height, as compared to10% at early head. Ether extract declines from 3.8 to 2.9%, and ashdrops from 11.1 to 6.3% at the same stages of harvest. Crude fiberincreases from 24 to 35% .

After extended weathering in the field after frost, a significant lossin dry matter in forage sorghum occurs, primarily in nitrogen-freeextract ("Webster and Davies 1956). Little change in percentage ofprotein was observed, but a significant increase in relative amountof fiber occurred. Burns and Wedin (1964) state that during afterfrost sampling of sudangrass, there was little loss in dry matter.

The composition of the sorghum plant depends on the conditionsof cultivation, including such factors as soil, fertilizer, climate, and plantpopulation. Eih"ich et al. (1964) found that when area per plant isdecreased, the dry weight per plant declines but total dry matter peracre increases. Protein and nitrogen-free extract diminish and fiberincreases in crowded plant plots. Quality, especially protein content,and yield can be improved by increased fertilizer application providedthat moisture and other factors are adequate (Burleson et al. 1959).

Proximate Analysis of Grain

Variations in Varieties and Hybrids.-The composition of sorghumgrain is comparable to that of other grains grown extensively for foodand feed. Like corn and wheat, sorghum grain is low in fiber and ash,because the glumes are readily removed from most varieties. Theprotein level ~f sorghum grain i~ slightly higher than corn or rice. Theoil content of sorghum is lower than in corn or oats, but is higher thanin rice, wheat, or barley. The ash content of sorghum is lower than incereals that contain attached glumes. Sorghum grain ranks next to cornin amount of total available energy among common cereal grains.

The composition of sorghum grains from grain, syrup, and foragevarieties was extensively investigated in several laboratories ( Hellerand Sieglinger 1944; Barham et al. 1946; Edwards and Curtis 1943).Ash ranged from 1.6 to 2.2%; oil varied from 3.1 to 4.9%; proteinvalues, from 11 to 15% . In general, grain sorghum kernels had higherstarch and lower fat contents than those of the smaller seeds of forageor syrup varieties. In a large number of waxy and normal grainsorghum selections analyzed by Horan and Heider (1946) no majordifferences were found in general composition.

·With the development of improved grain sorghum varieties and

122 SORGHUM PRODUCTION AND "{JTILIZATION

hybrids, irrigation, and fertilization, the grain has become larger,better filled with starch, and has a reduced protein content. In Table4.3 are tabulated the analyses of some hybrids and varieties grown inGuatemala (Bressani and Rios 1962). These data are expressed on a14% moisture basis. Ether extract presented no large differences amonghybrids or varieties, ranging from 3.1 to 4.5%. Crude fiber was ratherconsistent. Ash ranged from 1.4 to 3.9%; protein varied considerably,from 7.6 to 12.5%.

TABLE 4.3PROXIMATE A~D MI~ER,\L A~A"LYSIS OF SELECTED SORGHUM GRAI~SI

Ether CrudeProtein,2 Extract, Fiber, Ash, Calcinm, Phosphorus,

Sample C1 01~ C1 Mg % Mg C1

iC /0 /0 iC

HybridsRS 620 8.5 4.4 2.7 3.42 16.45 595RS 610 7.6 3.7 2.6 2.97 19.23 542HllX71 10.4 3.2 2.0 1. 39 22.31 238

VarietiesCombine

kafir-60 8.1 3.5 2.9 2.7·7 13.48 536Caprock 10.0 3.4 3.0 3.07 21.19 512Westland 9.0 3.3 2.6 3.73 45.53 1,097Norghum 9.0 3.9 2.8 2.43 17.18 479Martin 8.5 3.1 2.1 2.09 14.59 373Hegari 8.2 3.5 2.5 2.33 17 .12 416

1 All values expressed on 14% moisture basis after Brcssuni and Rios 0962).2 Protein = % N X 6.25.

The variation in grain composition may result from differences incomposition of the different parts of the grain; bran, germ, or hornyand floury endosperm. Bidwell et al. (1922) hand separated the partsof three sorghum grains-kafir, Dwarf milo, and feterita-and determinedtheir amounts and compositions. Among varieties the germ varied from7 to 11% of the kernel, and bran from 6 to 7%. Considerable differences occurred in levels of horny endosperm \vhich ranged from49 to 61%. As shO\vn in Table 4.4, Dwarf milo grain germ had ahigh content of oil, protein, and ash; 70% of the oil, 15% of theprotein, and 20% of the ash of this grain were in the germ. Next togerm, the horny endosperm had the highest content of protein. Endosperm contained less ether extmct and ash than other fractions. Starchyendosperm was richer in ether exh'act than horny endosperm. Thepericarp or bran fraction accounted for most of the fiber in the grainand contained some starch. Similar results were reported by Hubbard et al. (1950) on analyses conducted on grain parts from varietiesof grain sorghum cmrent at that time.

80111'('(': Bidwdl t!l HI-. (It'22).

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(;nEI\tI(~AL COMPOSI'1'10N OF '1'1n; 'Vn()Lli~ I·aatNli;L AND I'I'S PAHTS, FOU DWAHli' 1\11 LO SOUGH tIM

(Moisture-free Basis)

COIllpOIlent1'" rt of Kernel

'Vhole gl'llinBranIIol'llY eudospermSta rehy eudospermGerm

j'roportiollof Keruel,

(1/,'f)

100.05.5

5·1,.7~18. 7ILl

Ash,(If!o

I.RH~I. 07O.5li0.71H.,I,U

Ether Ex tl'll ct,0//0

9.fl4.990.150.2R

IH.H2

:Proteill,0//0

19.HH7 08

15. IIR !)I

20 R4

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Nitrogeu-freeExtl'llet,

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7R.7'!70. HiR9.,I,!)8H,QH'1,0.07

St" reh,0//(l

HR.5''!'l.liO

7'!.'H82.5

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8~....,"do(fJ

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"dt-<:>Z>-l;..

8Cl

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124 SORGHU:t\f PRODUCTION AND UTILIZATION

Kersting et al. (1961) follo\ved chemical changes in developingsorghum grain. The nitrogen content decreases slightly during thefirst 10 days after pollination and then remains constant at about 2to 3%. During gennination, sorghum grain changes in composition.Aucamp et al. (1961) found that in the sprouted grain used for maltthere is a decrease in fat and carbohydrate; protein remains the sameor increases slightly.

Agronomic Factors.-Soils and weather influence the yield and chemical composition of grain sorghums. Heller and Sieglinger (1944) notedin years of drought and high temperature that the yields of sorghumdecreased and that the protein level increased at the expense of starchand fat. Location greatly influenced variation in composition. Milleret al. (1964) conducted tests on different hybrids at eight Kansas locations. For single hybrids, such as RS 610, the protein content rangedfrom 7 to 10% at the test locations.

Crop management also is important in determining grain composition.As shown by Miller et al. ( 1964) grain that was grow'n on nonirrigatedland, continuously cropped, had an average yield of 2.0 tons per acreand 9..5% protein. In contrast, irrigated land produced 3.3 tons ofgrain per acre at a protein content of 8.3% . Miller et al. (1964) andBurleson et al. (19.56) demonstrated that protein content and yield ofgrain can be increased by nitrogen fertilization.

CARBOHYDRATES OF THE SORGHUM PLANT

Sugars and starches are the main storage forms of energy in thesorghum plant. Cellulose and hemicellulose conh'ibute to structuralcomponents in the plant.

Sugars in Stem and Leaf

Glucose and fructose are the predominant monosaccharides and reducing sugars in stem and leaf. Sucrose, a nonreducing sugar, is themajor disaccharide. Sugars are generally determined directly or onhydrolyzates of alcoholic exh'acts of plant materials by their reducingaction on copper or ferricyanide solutions. Smith (1962) used paperchromatography to separate and determine sucrose, glucose, fructose,and maltose in extracts of sorghum leaves and stems.

Varietal Variations.-Sugars in the stem are important commerciallyas a source of syrup and contribute to forage quality. The quantityand composition of juices and sugars in mature stem varv with the

COMPOSITION OF SORGHU}.I PLANT AND GRAIN 125

variety or the hybrid. Sw-eet sorghum fodders may contain 21 % totalsugars on a dry basis, whereas grain sorghum fodders have only 5 to 6%.

Extensive studies of the composition of sorghum juices from stemsof varieties produced for syrup or sugar have provided detailed information on the sugar content of these plants ( Webster et al. 1954;Ventre et al. 1948). Sucrose, the major sugar in the stalk juice of theripe plant, ranges from 6 to 15% with most varieties at 13%. Glucoseranges from 0.5 to 5% and fructose from 0 to 1.5%. According toEih-ich et al. (1964) in mature plants of Atlas sorghum, a forage variety,the level of reducing sugars exceeds sucrose.

Sugar contents of sudangrass varieties were correlated with grazingpreference. For the 10 varieties and hybrids tested by Gangstad (1964),total sugar content varied from 8 to 15%; reducing sugars ranged from2 to 4%.

Variations in Sugar During Development.-The content of the differentsugars varies as the plant develops. The increase in total sugars inthe plant between the dough to ripe stages is nearly double thatbetween the milky and dough stages. In the very young plant (40-45days) reducing sugars are highest in concentration (\Vebster et al.1948). Ventre et al. (1948) compared sugar contents of stalk juice atthree stages of growth of the plant. In the early stages the fructoseconcentrations were high and exceeded that of glucose in some varieties.In most sweet sorghums the sucrose level increases in the stem untilmaturity (\Vebster 1963). In contrast, in Atlas the sugar content ofthe stems may decline slightly during seed formation (Eih'ich et al.1964). Grain sorghums in early growth may have higher levels ofsugars in stems and leaves than sweet sorghums (Webster et al. 1948).However as the grain sorghums set heads, the sugar content of the stemdeclines precipitously. Sterile varieties in which the setting of seedis impaired have elevated sugar contents in forage parts (\Vebster 1963).

Regions of the stalk differ in sugar content; the center portion isthe richest in sugars. Ventre et al. (1948) noted that lower portions ofthe stem contain more glucose than sucrose. Sugar content and succulence of stem are reduced by crO\vding of plants (Eilrich et al.1964).

Sugars increase greatly, from 3 to 9%, in the leaves during theperiod 2 to 3 weeks after bloom of Atlas sorghum. A slight decreasein leaf sugar occurs as starch is deposited in the grain (Eih-ich et al.1964). Also, sugar content in leaves of sorgos and milos is subject todiurnal variation reaching a maximum in the afternoon and graduallydecreasing until daylight Qf the next morning (Miller 1924).

126 SORGHUM PRODUCTION AND UTILIZATION

Starch III Stem and Leaves

Starch is present in the leaves and stems of all sorghum varieties.In Atlas sorghum leaves, acid-hydrolyzable carbohydrates rise to 25%of dry weight shortly after bloom (Eih'ich et al. 1964). They diminishconsiderably as the grain develops. In stems, starch rises to about16% but diminishes also dming grain formation. In Atlas sorghum,starch is deposited in the culm after tl1e grain is mature. Smallamounts of starch are extracted along with stalk juices from sorgovarieties (Sherwood 1923). Sudangrass and sudangrass-sorghum hybrids contain starch in leaves and stems at all phases of growth (Gangstad 1964).

Hemicellulose in Stem and Leaf

Hemicelluloses are major components of plant cell walls and offibrous and parenchymal tissues. The hemicelluloses may consist ofpentoses, such as xylose and arabinose; sugar acids, such as glucmonicand galactmonic; and hexose sugars, such as glucose and galactose; alllinked by ,B-1,4-bonds. Hemicelluloses are extracted by strong alkalifrom tissues freed of sugars and starches. Hemicelluloses are chemically different from the a- or regular cellulose which is insoluble insb:ong alkali. Pentosans are hemicelluloses composed primarily of pentoses. They are determined by boiling tissues in concentrated hydrochloric acid and measming the fmfmal evolved.

Pentosan contents of stems of several varieties of sorghums are summarized in Table 4.5. Lengyel and Annus (1960) found that sweetsorghums have the lowest content of pentosans (20%), whereas ingrain sorghums, broomcorn, and sudangrass, pentosans are higher.Gangstad (1964) found that pentosan content in several sudangrassesranges from 20 to 23%.

The heads of grain sorghums are especially rich in pentosans. Pento-

TABLE 4.5CO~lPOSlTIO::-; OF SORGHUM PLANTS EXA~Il::-;ED FOR PULP PRODUCTIO::-;

Alcohol-BenzeneType of Cellulose, Pentosan, Lignin, Extract,

Sorghum % C1 C1 %/0 /0

Grain sorghurlls 29 24 16 7Broomcorns 39 24 15 SSweet sorghums 26 17 10 25Sudangrass ,13 45 16 4J ohnsongrass 42 27 17 5

Source: Lengyel and Annu, (1900).

COMPOSITION OF SORGHUM PLANT AND GRAL.' 127

sans constitute 32.8% of glumes or hulls removed from Leoti sorghum(Ed\vards and Curtis 1943).

In the course of extracting sugars from sweet sorghum, a methanolinsoluble material was recovered which inhibited crystallization ofsugars (Harris et al. 1952). Hydrolyzates of this hemicellulose gumyielded four sugars: glucose, galactose, arabinose, and xylose.

Cellulose in Plant

Cellulose is the major component of cell \valls and is responsiblefor most of the strength of fibrous tissues. Cellulose is a polymer ofglucose, but unlike starch which has a-l,4 and a-l,6 bonds, the glucose molecules are linked exclusively by ,8-1,4 bonds. Crude celluloseis generally determined as the residue of chlorinated pulps insolublein sodium sulfite. Crude cellulose may contain some pentosan and itsanalysis closely parallels the crude fiber analysis of sorghum foragehybrids (Stallcup et al. 1964; Proto 1962) .

. Variations in Cellulose Contents.-The crude cellulose analvsis of dif-"ferent types of sorghums is given in Table 4..5 (Lengyel and Annus 1960).

Sweet sorghum varieties contain less cellulose than grain sorghums orbroomcorn varieties. Also, mahlre sudangrass and johnsongrass exceedsweet sorghums in cellulose content. Proto (1962) reports that il:forage hybrids (Camelsorgo, Beefbuilder, Siloking, and Sll) containabout 29% crude cellulose. Leafy forage hybrids range from 24 to27% cellulose (Stallcup et al. 1964).

The content of crude cellulose does not vary greatly during thedevelopment of the plant (Bettini and Proto 1960). The content ofcellulose is higher in the stem than the leaf. The stalk rind is higherin cellulose (34%) than the pith (19 %) (Stallcup et al. 1964).

Sorghum Cellulose for Paper.-The amount and quality of cellulose insorghum stalks have encouraged their investigation as possible pulpsources for the paper industry. The a-cellulose in sweet sorghum stemresidues from syrup manufacture accounts for .35% of the dry weight;pentosans, 27%; and lignin, 20% (Sorgato 1949). A good yield ofcrude cellulose suitable for pulp is obtained upon h'eatment of theground-pressed stalks with 2 to 5% NaOH at 120°C for 3 hI'. Seventyfive percent of the lignin is removed in such processing.

Escourrou (1959) concluded that the bagasse from sugar sorghumswas not the most productive sorghum source of cellulose because oflower yield and h'ansportation, storage, and processing problems. Heinvestigated the yields of fiber obtained directly from numeroussorghums. Several varieties of broomcorn sorghum, prinCipally of the

128 SORGHU~f PRODUCTION AND UTILIZATION

Evergreen type, yielded e~cellent pulps in good quantity. Johnsongrass,while yielding lesser quantities of cellulose ,vas desirable becauseof its perennial regrowth. The broomcorn was planted at a high densitypopulation and produced 7 to 11 tons of crude cellulose per acre.

Fibers of sorghum pulps are shorter in length (2,000 p.) than thoseof coniferous and hard woods (3,000 p.), but are longer than those ofother leafy species (1,000 p") (Escourrou 1959). They have smallerdiameters, 16 p., as compared to 40 p. for pine fibers. The high lengthto-diameter ratio permits sorghum fibers to serve as a reinforcementagent for other fibers in paper as they fill interstices well. X-ray examination establishes that even after sulfite processing, the celluloseof sorghum fiber retains a high degree of molecular orientation. Consumption of soda and chlorine bleaches is low for preparing sorghumpulps. Burst resistance, folding strength, and other characteristics ofpapers fabricated from pulps of sorghums of various types are satisfactory (Lengyel and Annus 1960; Escourrou 1959).

Starch in Sorghum Grain

Starch Analyses.-Cereal grains including sorghum are valued for theirhigh content of energy in the form of starch. Starch content in defatted sorghum grain meals may be detennined as reducing sugarafter enzyme and acid hydrolysis. Also, the starch may be solubilizedand determined by its rotation of polarized light. The specific rotation, [a]D' of sorghum starch is 20.3.1 to 203.5, whereas that for wheatstarch is 202.7 to 203.2 (Patel et al. 1960) . Using these procedmes,Edwards and Curtis (1943) found that starch constihlted 68 to 73%of the grain from 20 varieties of grain and syrup sorghums. The starchcontent was highest in milos and kafirs and lowest in the sorgos. Kernels of grain sorghum hybrids (RS 626, TE 77, and OK 612) grownin 1967 with nitrogen fertilization and irrigation had starch contentsvarying from 74 to 76%. Starch comprises 83% of the endosperm,13.4% of germ, and 34.6% of the bran obtained by hand dissectionof sorghum grain (Hubbard et al. 1950).

Amylose and Amylopectin Content.-Different types of starches arefound in sorghums and other cereals. One kind of starch, amylose, isa polymer of glucose units united exclusively by a-l,4 linkages to givea linear chain (Fig. 4.1). It complexes with iodine to yield a bluecolor. Amvlose dissolves with difficultv in water, from which it maybe precipit~ted by butanol. The fracti~n of starch that is more solublein water or an aqueous butanol solution is amylopectin. Amylopectinhas, in addition to a-l,4 linkages, about 5% of a-l,6 bonds that give

COMPOSITION OF SORGHU:YI PLANT AND GRAIN 129

a branched or bushy structure (Fig. 4.1). It gives a red color withiodine. Both of these starches have large numbers of anhydroglucoseresidues in their chains; amylose molecular weights range from 2 to7 X 105 while amylopectin molecules are higher in molecular weight,1 to 10 X lOG (Foster 1965).

Amylose may be determined in starch solutions either by amperometric titration with iodine or by photometric estimation of the blue

(H20H (H20H (H20H (H20H (H20H (H20H (H20H (!:hOH

~'I!l~'I!l~'I!l~'I!l~'I!l'LlirO'I!l~'I!l~'I!l'I(.--~~~~~~~~--'I(.

H~ H~ H~ H~ H~ H~ H~ H~

Amylose

AmylopectinFIG. 4.1. ivIOLECIJLAR STRUCTURES OF AMYLOSE AND A:-'IYLOPECTlN

color formed with iodine. Deatherage et al. (1955) found that innormal varieties of grain sorghum, amylose content of starch rangedfrom 23 to 28%; amylopectin comprised the remaining starch. Nosorghum grain was found to be high-amylose, above 28%, in contrastto com where high-amylose strains have been developed. Starch inwaxy sorghum varieties is essentially all amylopectin.

Starch Granule Characteristics and Gelatinization.-As seen in Fig. 4.2,starch granules from sorghum endosperm are in about the same sizerange as those from com (6 to 24 p- diam), but on the average, starchgranules of sorghum are slightly larger, 15 /L, as opposed to 10 /L forcorn (Schoch and i\Iaywald 1956). Granules in sorghum pericarpare much smaller. The starch granules in sorghum horny endosperm are

130 SORGHU?lr PRODUCTION AND UTILIZATION

Corn Sorghum Wheat

Normal WaxyFrom MacMasters et al. (1957)

FIG. 4.2. STARCH GHA:',TLES: (UPPER) STAHCH GH.-L'mLES OF COHC'i. SOHGHU:'-r.

AC'iD \VHEAT; (LOWER) GELATlC'iIZED STAHCH GRAC'iULES OF NOR:'-IAL "AC'iD \VAXi:

SOHGHU:'-[

COMPOSITION OF SORGHUM PLANT Al'i1) GRAIN 131

polyhedral and packed in close order, whereas in the floury endospermthey are round and more randomly spaced (\Iadvlasters et al. 1957).The densities of sorghum starches are about 1..S gm per ml (Barhamet al. 1946).

On heating in water starch granules undergo gelatinization or disruption of their internal organization; they lose their birefringence,absorb water, and swell (Fig. 4.2). Gelatinization temperatures ofsorghum starches extend from 68° to 76°e from initiation to completegelatinization. On the other hand, gelatinization of corn starch occursat 62° to noe (Leach 196.S). Gelatinization temperatures are relatedto granule characteristics, such as average diameter, density, and amountof adsorbed substances, but are only slightly affected by amylose content.

Breakdown of starch by enzymes is more rapid \vhen the granuleis gelatinized. Novellie and Schutte (1961) used rate of amylolysis ofsorghum starch as a means of estimating degree of gelatinization.Sodium chloride decreases the rate of gelatinization. Isolated sorghumstarch gelatinizes more readily than does that in the grain.

A lower gelatinization temperature of sorghum starch would be desirable. Heusdens and King (1962) in studies of 125 sorghum introductions found several nonwaxy and waxy selections in which thestarch had lower gelatinization temperatures. Those for some kaoliangvarieties ranged from 63° to 71 °C. Heusdens and King (1963) alsofound that gelatinization temperatures of grain sorghum starch increasedP to 3°C when seed was stored over a period of 1 yr. Also, climaticconditions in the field influence gelatinization temperature.

'When heated in water, waxy starch granules swell more rapidly thanthe nonwaxy (Fig. 4.2). This difference in granule behavior is due tothe absence of the linear starch fraction in waxy sorghum. Swellingpower is measured by the weight of sedimenting wet gelatinized starchobtained when starch is heated in water under prescribed conditions.Swelling powers of ordinary corn, sorghum, and rice starches are 24,22, and 21; whereas that of waxy corn, sorghum, and rice starches are63,49, and 46, respectively, at 95°C (Leach 196.5).

Phytoglycogen.-Watson and Hirata (1960) determined the starch content in sugary milo, feterita, and other sorghum grains (Table 4.6).In tlle sugary milo variety, the content of starch was only 31..5%. Awater-soluble carbohydrate constituting 28.4% of the grain \vas extracted from it with 10% trichloroacetic acid. This polysaccharide resembled phytoglycogen from sweet corn. Phytoglycogen containsa-glucose residues, but is more highly branched than amylopectin andof lower molecular weight.

Soul'ee: Aftel' \ValHoll alld Hirata (HHiO).

Grams per 100 (;m Grain, Dry Basis

TAIl],I'; 4.U

CAltIlOIlYIlHA'l'I<lS IN GHAIN SOHGlIlJMS

Variety

Combine kafir 54,'1'Waxy kafir\Vaxy ka fir, whiteSugary reteri taSugary milo

Genotype

Wx Suwx Suwx Su\Vx suWx su

Starch

un.nHn.:IH8.H5H.7~1I .5

Water-solu blePolysaccha ride

7.n'l8.4

Sugar Fruetose Glucose Suerose Maltosc Rafliuose

1.15 0.05 0.()4. 0.84, 0 0.1:1I.:ln O.B O.B 0.n5 0 0.121.07 o.on O.OH 0.77 0 o.on~l. UH O. ~l8 O. ~l'l, I.H7 0.05 O. I~l

2.HH 0.05 0.22 2.~ 0.02 0.1

f-'Wt-:l

[J)

of5II:C.!?....

~t:IC.n....,.....oZ;JZt:I

C.

~N;J-gZ

COMPOSITION OF SORGHU?\1 PLANT AND GRAIN 133

Sugars in Sorghum Grain

Sugars translocated from the green parts of the plant are the precursors of the starch deposited in the grain. Kersting et al. (1961 )followed the change in sugar and starch content that occurs duringgrain development. Sugar content rose until 12 days after pollination to a level of about 10% of the grain. It then dropped until at20 days it reached 1% . However, the amount of sugar per kernelremained fairly constant (0.25 mg) until maturity. Concurrently, thestarch content of the grain rose sharply after 5 days to a level exceeding60%. After 35 days the starch and sugar content dropped slightly;this drop indicated a continuation of physiological activity after maturity.

A sugary mutant was reported by Karper and Quinby (1963) tohave higher levels of sugars at all stages of development. At the milkdough stage it had 30% sugars versus 15% for the normal, and at themature stage, 3.9 and 1.9% for sugary and normal, respectively.

The sugar content of mature sorghum grains ranges from 0.9 to 2.0%in normal varieties (Edwards and Curtis 1943). Using paper chromatography and chemical derivatives, Nordin (1959) identified in grainsorghum extracts the trisaccharide-rafFinose-and the tetrasaccharidestachyose-in addition to sucrose, fructose, and glucose. \Vatson andHirata (1960) determined the amounts of sugars in several sorghumgrains, including waxy and sugary types (Table 4.6). Sucrose, themajor sugar in all varieties, is also the sugar that increases most insugary grains. Sugary feterita had a higher content of fructose thanany of the other varieties. Raffinose content was about the same inall grains.

Nordin (1959) followed changes in sugars dming gem1ination ofsorghum grain. Sucrose concenh'ation initiallv declined at 36 hr butthen increased. Glucose and oligosaccharide~ showed increases onlyafter 36 hr.

Hemicelluloses in Grain

In the whole sorghum grain, pentosans account for 2 to 3% of dryweight in a number of varieties analyzed by Edwards and Curtis (1943).Almost all the pentosans present are in the pericarp or bran, In thisrespect, sorghum resembles corn.

PROTEINS It\' SORGHUM GRAIN AND PLANT

In sorghum there are a variety of proteins that exhibit different physical properties, biological activities, and nutritional values. Although

134 SORGHD:\I PRODUCTION A:\1) UTILIZATION

only 20 different amino acids are common constituents of plant proteins,they may be joined in different proportions and sequences to formlarge protein chains. The shape, solubility, digestibility, and nutritivevalue of protein molecules depend on their amino acid compositionsand arrangements. Since many amino acids cannot be synthesized byhumans, nonruminant livestock, or poultry, they are essential constituents of life-sustaining diets. The advent of automatic amino acidanalyzers for analysis of acid hydrolyzates of protein has facilitated arapid expansion of information on sorghum proteins.

Types of Proteins in Grain

On the basis of his observation that several different solvents usedin sequence are required to remove almost all the protein of cerealgrains, including sorghum, Osborne (1924) classmed these proteinsinto: (1) albumins, soluble in water; (2) globulins, soluble in solutions of salts; (3) prolamines, soluble in solutions of ethyl alcohol; and(4) glutelins, soluble in dilute alkali. The greatest part of sorghumproteins are not extracted with water or salt solutions.

Albumins and Globulins.-Although small in quantity, the albumin andglobulin fractions of sorghum proteins include enzymes and otherbiologically active substances. Jones and Csonka (1930) extracteddefatted meals of 3 varieties of sorghum (a kafir, a milo, and a feterita)with 10% sodium chloride solution. They recovered only 12.7 to 13.3%of the totalnih'ogen of the meals in the extracts. Virupaksha and Sash'y( 1968) subjected endosperm meals from several sorghum varieties toexh'action with water and then 1% sodium chloride solution. From2 to 8% of the proteins from the different grains was removed by waterwhile an additional 2 to 10% was exh'acted with salt solution (Table4.7). Albumins and globulins can be precipitated from solution with50% ammonium sulfate to yield fairly pure protein fractions.

T"\BLE 4.7SOLUBILITY FRACTIO);ATIO); OF PROTEI); OF GR"\!); SORGHU~1 E);DOSPERM

Variety

ProteinContent

(Endosperm),c:c Albumin

% of Protein

Globulin Prolamine Glutelin

M-35-1 SiruguppaBS-81-3 AnnigeriCSR-1 Bijapur160 Cernum361 Dochna

9.9410.5618.1317.0619.0

5.65.47.7.1.21.3

7.37.36.49.3:2.0

3:2.656.:243.144.558.8

37.434.6:26.834.619.0

Source: Virupaksha and Sastry (1908).

COMPOSITION OF SORGHUM PLANT A-,.'\11) GRAI.e" 135

Albumin and globulin fractions each consist of many different proteins. Sastry and Virupaksha (1967) used polyacrylamide gel discelecb'ophoresis to separate the proteins in both water and saline exh'actsof sorghum. Under the influence of an applied voltage, the variouscharged protein molecules migrated at different rates through the gelsin buffered solutions. Several distinct bands of proteins stainable \vithdyes were detected in the gel after electrophoresis of the water or 1%sodium chloride exh'acts in pH 4.6 alanine-acetic acid buffers,

The amino acid composition of the globulin fraction of sorghumendosperm proteins determined by Virupaksha and Sastry (1968) isgiven in Table 4.8. Levels of lysine, threonine, arginine, methionine,

TABLE 4.8,un"o ACID COMPOSITIO" OF PROTEI" FRACTIO"S OF A SORGHU~I GRAIN (cSH-l BIJAPUR)

(Percent of Protein)

Protein Fraction

Amino Acid

LysineHistidineArginineAspartic acidThreonineSerineGlutamic acidProlineGlycineAlanineHalf cystineValine'MethionineIsoleucineLeucineTYrosinePhenylalanine

EndospermMeal

1.72.163.256.253.814.5

29.7510.313.27

12.581. 087. ~25

1. 514.91

16.584.646.4

Globulin

3.361.456.148.68'1.875.55

15.85.336.256.741. 996.462.243.456.724.014.77

ProIa mine(Kafirin)

0.140.670.666.72

3.3225.0711.63

1. 2813.96Trace

5.881.335.04

15.335.175.84

Glutelin

3.123.125.919.074.885.38

24.0814.865.339.41. 215.5

4.0712.493.234.9

Source: Virupakshn and Saslr,Y (I96S).

and aspartic acid are much higher in the globulin fraction of sorghumproteins than in the total protein of the endosperm.

Kanrin.-The predominant proteins in the grain are prolamines oralcohol-soluble proteins. Unlike corn from which zein is readily extracted with 70% ethanol, little protein is exh'acted from sorghummeal with that solvent at room temperature. However, solutions ofboiling 70% ethanol yielded 67% of the total protein of the kanr mealin experiments by Jolms and Brewster (1916). Protein was precipitatedfrom this solution by addition of sodium chloride and was designatedkanrin. To avoid coagulation or denaturation of the protein, later


workers maintained the extraction at 60°C (Jones and Csonka 19.30).In a study of 6 varieties, Virupaksha and Sastry (1968) found thatprotein soluble in hot 60% ethanol accounted for 30 to 60% of thegrain protein (Table 4.7). The kafirin fraction is composed of at least7 different components as indicated by bands after electrophoresis onpolyacrylamide gels in pH 3.1 aluminum lactate buffer (Sastry andVirupaksha 1967).

Like zein from corn, kafirin is poor in nutritional quality, since itis deficient in several essential amino acids as shown in Table 4.8 fromdata by Virupaksha and Sastry (1968). The amount of lysine, arginine,histidine, glycine, and methionine is low in kafirins. Glutamic acidcontent is high, but it probably occurs primarily in the proteins as itsamide glutamine, as indicated by a large amount of ammonia in acidhydrolyzates. The nonpolar amino acids-leucine, proline, and alanineare also prominent components of kafirin. The solubility of kafirin inorganic solvents, such as 60% ethanol, is due to its high content ofthese nonpolar amino acids and its low content of charged amino acids,such as lysine. Kafirin is low in tryptophan.

Glutelin.-Glutelin is the second major protein fraction. After removing saline and alcohol-soluble proteins, the meal is stirred with0.4% sodium hydrOXide for 2 hr at room temperature to extract theglutelin. From 20 to 40% of the meal protein, depending on the varietyof sorghum (Table 4.7) was isolated in this manner (Virupaksha andSastry 1968). The insolubility of glutelins in neutral solvents has beenath'ibuted to their high molecular weights caused by disulfide bonds inthe amino acid cystine, which chemically link different protein chains.These bonds are labile to alkali. The glutelin of one variety of sorghum(CSH-1 Bijapur) has been analyzed for amino acid content by Vil'upaksha and Sastry (1968) who report that it has a higher contentof lysine, histidine, arginine, and glycine than the kafirin (Table 4.8).

Since lysine, threonine, and methionine are esscntial amino acidsmost deficient in cereals, it is evident from Table 4.8 that thealbumin and globulin proteins are the best in nutritional value; kafirinis the poorest, and glutelin is intermediate. The large amount of kafirinis responsible for the low nutritional value of sorghum grain protein.In comparing the protein dish'ibution in grains of different varietiesvarying in protein amount (Table 4.8), Virupaksha and Sastry (1968)observed that a high content of kafirin generally accompanied highlevels of total proteins. Although the protein level was enhanced, theprotein nutritional quality was diminished. However, in the variety160 Cernum, the increase in protein content was also accompanied by

COMPOSITION OF SORGHU~r PLANT AND GRAIN 137

a greater increase in the proportion of albumins, globulins, and glutelinsthan kafirin.

Development and Distribution of Proteins in Grain

In Table 4.4 it is seen that the different parts of the grain (germ,endosperm, and bran) differ in amount of protein. The grain parisalso differ in their proportion of the different types of proteins. Theprolamines are practically absent from the gen11 and hull, whereasthey predominate in the endosperm. Consequently, germ proteins arehigher in nuh'itive value than those of endosperm. The essential aminoacids-lysine, threonine, methionine, and cystine-are present in thegerm protein at levels of 4.1, 3.4, 1.5, and 1.0%; w'hereas in endospermprotein they account for only 1.1, 2.8, 1.0, and 0.8%, respectively(Pickett 1967).

The aleurone layer of endosperm is rich in albumins and globulins.Just inside the aleurone at the periphery of the horny endosperm is adense layer of cells rich in kafhin ("Watson et al. 1955). The largeramount of protein in the peripheral region of the endosperm is evidentin Fig. 4.3 (\Vall 1967). This illustration sho\'/s a photomicrographof a section of sorghum grain from \vhich the starch was removed

From Wolf and KllOO (in Wall 1967)

FIG. 4.:3. SECTION OF SORGHU.'>I GRAIN SHOWING PROTEIN 'MATRIX AND PHOTEIN

BODIES. STARCH RE.'>WVAL BY TREAT.'>lENT WITH a-A.'>IYLASE


by amylase treatment. It reveals a network of proteins in whichsmall subcellular bodies are located. These bodies are presumed tobe sites of storage of kafirin. The matrix protein in which the protein bodies and starch are embedded may consist of glutelin. Theinsolubility of most of the endosperm protein and the manner in whichthis protein binds the starch granules contributes to the difficulty ofdigesting sorghum grain. Also, this cellular organization must be disrupted to facilitate starch-protein separation by wet-milling.

As the grain progresses from the milky to the mahIre stage, thereis a rapid increase in the amount of alcohol- and alkali-extractableproteins. In conh'ast, the albumin and globulin proteins, which inthe early stages of seed development predominate, constihIte a smallerfraction of the total protein of the mature seed (Taira 1964). As theseed ripens, alanine, isoleucine, leucine, glutamic acid, phenylalanine,and proline increase while lysine, glycine, aspartic acid, and argininedecrease.

Effect of Agronomic Factors and Variety on Protein

Fertilizer use and location of planting not only affects protein level,but also influences the amino acid composition of the protein. 'Waggleet al. (1967) found that nih'ogen fertilization linearly increased theproportion of glutamic acid, proline, alanine, isoleucine, leucine, andphenylalanine in the protein while that of lysine, histidine, arginine,threonine, and glycine was reduced. Nih'ogen fertilization evidentlyfavors increased deposition of kafirin in the grain. Variations inprotein content due to location also were shown to influence theamino acid content of the grain.

A major factor that detenl1ines tlle amino acid composition of theprotein of sorghum grain is variety and hybrid. Analysis of 15 differenthybrids grown at two locations by Deyoe and Shellenberger (1965)showed variations in protein content, and demonstrated significantdifferences in amino acid composition of the protein. Some of theirresults are given in Table 4.9. The correlations of lysine, arginine,and glycine to amount of protein \vere negative. (Waggle and Deyoe1966). Apparently in hybrids developed in tlle United States, increasesin protein content have so far resulted in higher levels of proteindeficient in certain essential amino acids.

Virupaksha and Sastry (1968) examined sorghum grains of 44 varietiesfrom the 'World Collection and of 5 hybrids for protein and for lysine.Protein values ranged from 8.5 to 18.2%. In general, they also established a correlation between high-protein content and a low proportion

TA Ill"l" 4.!lCO!\IPAHISON Oli' AMINO ACID ANALYSleS OF SOnOllU~1 GUAINS, O'J'llNn CmHli}ALS, ANn S()Yln~AN MRAL 'VI'l'1I I'~AO PHO'l'I~lN PA'I"I']i1HN

(Pereent. or PI'Ot.ein)

Sorghnms

Amino Aeid ItS lil0 ' 5!l-MIP._------

Lysine 'l.1 1.8Histidine 2.2. 'l.OArginine 2.8 ~l. ()Aspart.ie aeid (Ui li.O'flll'eoiline ~L '2 ~l. 0Leueine 4,. ,~ .... ~l

Glut.amie aeid ~tl. !) 21.!lProline 8.1 7.7Glyeine B.B 2.nAlanine n.5 0,5Hall' eysLine 1.1 1.0Vllline 5.2 4.7Met.hi(Jlnine 1.5 I. IiIsoleueine ~l . H ~l. 8Leneine 1:1.:1 I~l . H'rvl'osine I.li ).')'

Phenylalanine 5.0 ,I,. HTrypt.ophan ).0 1.0(j{l J>rotein 10.0 10. I

1 De.vtJt~ and Shdlt'll!Jel'g't'l' (I1HI5).2 Vil'upaksha Hlld Sast!'y (I~Hj8).

:1 Unpuhlished dat.a hy 1Il1thol's•

.\ Nationul Aeudem,\- of SeielH't's (1\)58),fJ JlH(~ki:-; d (//. (HWI).,; FAO/WIlO (l\ln5).

CSH-P HiO Cernum2 Corn" Wheala--~~ ..-

1.7 B.l ~.7 2.5'l.O 2.. ~.~ ~l. OB 'l.O2.U 4.H (). ~l :l.liH.2 H.l li.8 ~l. 4~L Q :1. li B.li ~l. [;4.7 4.7 5.2- ,t.7

2:1.li 'lao ,I, 'll .B ~2H . ~.~

8.li 12.7 10.0 1O.a2.8 8. ~l 4.0 :1.,1,

1:1.5 1O.B 8.1 :1.0_.. - ] . (i 4.05.,1, ;1,. '2 '(,,7 '2. nO. 8~1 1.1 1.7 1.0S.7 B.8 :1. Ii 4. 'l

I:Ul H.7 1'l.4 (i.liI.!l '2. "1 '~. ,I, :~ ()

5.1 'I,.li 5.0 4.!l1.0

l(i. Ii 17.7 10.0 l'l.O

Riel'''

:1.4,2.22.

:1. ,~

1.2(;.21.,1,5.28.'25.75.'!

!l.0

FAOProvisional

Soyhelln MellI" PaUt,rnH

li.H ·1,.:12.08. ,~

12.li4.:1 B.:l5.H

21.0li.O4.5,I,. :;

1. (i 1. 75..1- 2.81.7 1.75.1 ,Ul7,7 ·t.!)~L!) l!. {):;.0 2.!l1.:1 I. 1

(iIA

()o7'Mhjo[Jl

SoZ

~[Jl

ggC1/~

~;,.."'.>-l;,..

8o;U;,..Z

f-'eNU

140 SORGHU~I PRODUCTION AND UTILIZATION

of lysine in the protein. However, a marked exception from this trendwas exhibited by the high-protein variety 160 Cernum (Table 4.9).In corn, high-lysine varieties have been discovered that have a changedprotein composition, less zein, and more of the other components (Mertzet al. 1964). This observation has encouraged exploration for highlysine sorghum varieties.

Nutritional Value of Grain Protein

How does sorghum grain compare with other cereal grains andplant seeds in amino acid composition? Table 4.9 summarizes theamino acid content of the protein in several cereals and soybean meal,and compares their analysis to the FAO recommendations for essentialamino acid composition of a balanced protein in human diets. Theprotein of hybrid U.S. sorghum grain is low in lysine, threonine, methionine, and tyrosine. It is also low in arginine, histidine, and glYCine,which are essential for some animals. The tryptophan level is near theminimal requirement but is higher than that of corn.

Cereals are generally supplemented \vith a suitable protein source,such as defatted and properly toasted soybean meal (Table 4.9), toprovide the level of protein required in formulations for optimumgrowth of young nonruminants and for nutrition of preschool children.For example, soybean meal is often added to sorghum rations toprovide an adequate level of lysine and threonine, but methioninethen becomes the limiting amino acid in the formulation.

Proteins in Stem and Leaf

Because the vegetative part of the sorghum plant is primarilyused as fodder for ruminants, less attention has been given to its protein components. Klimenko and Goldenberg (1960) extracted proteinsfrom the stems and leaves of several hybrids and varieties of sorghumwith 7% sodium chloride and then with 0.2 M sodium hvdroxide.From .35 to 45% of the nih'ogen was exh'acted with these reagents.From 67 to 76% of this protein was soluble in the saline solution;the rest was exh'acted bv the alkali. About 2% of the extractednitrogen was nonprotein nih·ogen. Amino acid analysis of leaf proteins from various cereals indicate they have suitable levels of allessential amino acids.

LIPIDS

The lipids in sorghum are important to animal and human nutritionbut may contribute to the development of off-flavors and rancidity


in sorghum-based food products. Two general types of solvents areused to extract lipid material from sorghum. Nonpolar solvents, suchas hexane, extract principally triglycerides with lesser amounts ofhydrocarbons, sterol esters, fatty acids, monoglycerides, diglycerides,and sterols. This mixture is usuallv termed crude fat or oil. The

-more polar solvents, such as n-butyl alcohol or chloroform-methanol,extract fatty aCids, phospholipids, glycolipids, and lipoproteins. Newermethods of analysis, thin-layer and gas-liquid chromatography, makeit possible to separate rapidly and identify components of these complexcrude lipid mixtures.

Grain fat or oils normally contain relatively low concentrations offree fatty acids. The major portion of fatty acids are combined inmono-, di-, and triglycerides and in phospholipids. For ease of analysis,these fatty acids are liberated from parent compounds and convertedto more volatile methyl esters. The fatty acid methyl esters may thenbe separated by distillation or by gas-liquid chromatography. Chainlength and degree of unsaturation of fatty acids determine the physicaland chemical properties of the oils. The extent of unsaturation (iodinenumber) affects the nutritional value and storage stability of the oil.

Grain Lipids

The distribution of nonpolar lipids in five varieties of sorghumgrain and their hand-dissected fractions closely resembles that of corn(Hubbard et aZ. 1950). Average oil content of the whole grain is3.6%, with oil contents of the endosperm, germ, and bran, 0.6, 28.1,and 4.9%, respectively. The endosperm contains 13% of the totaloil in the kernel; the germ, 76%; and the bran, 11%. The petr'oleumether extract from sorghum bran consists mostly of wax rather thanoil. Compositions are similar among the five varieties.

Nonpolar Lipids.-An examination of nonpolar lipids from groundwhole sorghum grains of three varieties by thin-layer chromatographyindicated the presence of a number of different classes of substances(\Vall 1967) (Fig. 4.4). The largest single fraction was composedof triglycerides. Smaller amounts of hydrocarbons, sterol esters, fattyacids, monoglycerides, diglycerides, sterols, and phospholipids werealso present. The tr'iglycerides were further separated by gas-liquidchromatography. The 3 sorghums had similar triglyceride compositions averaging as: C50 , 3%; C52 , 32%; C54 , 64%; and C56 , 1%.Subscripts refer to the total number of carbon atoms in the threefatty acids esterified to glycerol in the triglycerides.

S~veral investigators have determined the physical properties and

142 SORGHC\[ PRODUCTION AND UTILIZATION

Thin Layer Chromatogram

Hydrocarbons+ Sterol Esters

Triglycerides .

Unknown BFatty Acids

_Unknown A-Sterols- DiglyceridesPhospholipids

CommercialMixture

Combine7078

Martin

From Blessil! (il! Wall 1967)

FIG. 4.4. THl:-i-L-\.YEH CHHO:\L\TOGHAPHIC SEPAHATlO:-iS OF SOHGHUM NO:-i

POLAH LIPIDS FHO:\{ THHEE DIFFEHE:-iT SORGHUM GRAD,S

composition of sorghum grain oil (Table 4.10). Kummerow' (1946A, B)analyzed oil after extracting ground, wax-free, whole grain, whereasBertoni and his cO\vorkers (1963) examined only germ oil. The originof the oil investigated by Denisenko and Volkova (1960) and Durioet al. (1965) was not specified. Sorghum grain oil was slightly lesssaturated than corn oil and contained more oleic and stearic and lesslinoleic, myristic, and hexadecenoic acid than corn oil (Kummerow1946A, B). Kummerow (1946A, B) also reported that neither corn norsorghum grain oil contained linolenic acid or fatty acids above CIS,whereas Denisenko and Volkova (1960) and Bertoni et al. (1963 )found that sorghum grain oil had from 1 to 2% linolenic acid.

Baldwin and Sniegowski (1951) studied the fatty acid compositionof lipids associated with four main fractions from wet milling ofcommercial hybrid sorghum. These fractions included germ (52%fat), starch (1% fat), gluten (7% fat), and fiber (3% fat). Fattyacids were analyzed by fractional distillation and spectroscopic tech-

PIlOPgU.'I'I]i:JS ANn COMPOSI'I'I()N OIi' SOHGIIUM GllAIN OII~

'rAULI' 4.10

Propcrty or Componcnt

ColorRcfractivc indcx (25°e)Unsaponiliablc mattcr ('Ii,)Acid valueSaponification valucIodinc valueThiocyanogcn valucAcctyl valueNcutmlization cquivalcntL:wric acid (%)Myristic acid (%)Palmitic acid (';;;,)llexltdeccnoic acid (%)Stcaric acid (%)Olcic acid (%)Linolcic acid (%)Linolcnic aeid (%)

Durio elal.(llH;5)

0.20.4

IH.21.92.0

HO.540.7

2.0

Dcniscnko andVolkovlL (llHiO)

4'!. ,j,81.15

Knnllnerow(I!H(;A)

1.47181.88H.14

181.0110.07(;.71(;.7

0.28.H0.]5.8

3(;.2~.4

Authors

Kummerow (1!l4oliB)

Light ambcr to grccnI.4(i!l52.51

I'W.881.5

278.8

7.8

,1,.730.5'W.5

Bcrtoni el ai. (l!)(;H)

1.47202.88

IS.!J18!J.5121. '!

Total saturatcd acids, ]8.!J

Q5.n52.S

1.0

8y

~o'"8o~

o"1

'"o~II:C.y...,"dt"";;...Z>-1

;;...

8(')::n;;...~

...........W


niques. Gluten and germ fats had approximately similar amountsof oleic and linoleic acids, but more polyunsahlrated fatty acids werepresent in the gluten. Gluten and fiber fats contained up to 10%unsaponifiables and about 20% free fatty acids.

The lipids associated with starch influence paste clarity and starchinsolubility. The fat content of sorghum starch by methanol extraction is 0.32 %, and by acid hydrolysis, 0.72% (Lindemann 1951).Starch fat is 90% free fattv acids. It contains less of the unsaturatedacids, oleic and linoleic,' with correspondingly higher amounts ofsaturated acids, primarily palmitic, than does germ, gluten, and fiberlipids. The composition of fats in sorghum starch is similar to that incorn starch.

'Vax.-Sorghum grain contains approximately 0.25% wax (Kummerow1946A) . The wax content of sorghum grain is 50 times more thanthat of corn. The wax is easily removed by eXh'acting the ungroundgrain with hot hexane. The characteristics of waxes from four varietiesof sorghum grain were compared by Bunger and Kummerow (1951)with those of carnauba wax for possible industrial use. Sorghum grainwax has an acetyl value of 7; acid number, 13; iodine number, 18; andsaponification number, 30.

The composition of sorghum grain wax was studied by fractionatingit on columns of h'icalcium phosphate and silicic acid (Dalton andl\Iitchell 1959). Of the material recovered from the columns, approximately 5% was paraffins, 49% esters of long chain fatty alcohols, and46% free alcohols. Melting points, X-ray diffraction studies, andinfrared absorption spectra indicated that each of these fractions wasa mixture of related substances rather than a single compound. Chainlengths of the individual paraffin hydrocarbons, alcohols, and fattyacids were mostly 26, 28, and 30 carbons.

Phospholipids.....:Major components of the bound lipid fraction extracted from sorghum grain with methanol-chloroform are phospholipids. These substances represent about .5% of the total lipids. Boissyand Perles (1965) fractionated half of the phospholipid into a 95%ethanol-soluble lecithin fraction; the remainder constituted the cephalinportion. The lecithins consist of glycerol, fatty acids, phosphorus, andcholine associated by ester linkages. Thin-layer chromatography of thecephalin fraction revealed the presence of phosphatidylethanolamine andphosphatidylserine, compounds which resemble lecithin except tllat choline is replaced by ethanolamine or serine. An inositol phosphatide wasalso detected on the chromatogram. This compound contained phosphorus, glycerol, inositol, and fatty acids in the proportion 1: 1 : 1 : 2.

COMPOSITION OF SORGHUl\I PLANT AND GRAIN 145

Leaf and Stem Lipids

Lipids in the leaf and stem of sorghum have received limited attention despite their importance in forage. Fractionation of the lipidsof hexane and acetone extracts of sorghum leaf and stem by countercurrent dish'ibution yielded five distinct components (Burnett et aZ.1958). The amounts of phosphorus in various fractions were 0.04 to1.20%; of nih'ogen, 0.08 to 1.23%. Fatty acid composition of the fractions was determined by gas-liquid chromatography following theirconversion to methyl esters (Burnett and Lohmar 1959). The majorunsahu'ated acid was linolenic, which \vas concenh'ated in the morepolar fraction. The major saturated acid, palmitic, was relatively evenlydish'ibuted throughout the fractions. The chief acid of the leaf andstem was linolenic. Sorghum leaves and stems are lower in linoleicacid and much higher in saturated acids than other leaf fats. Apparently the fatty acids of sorghum leaf and stem are present largelyin phospholipids, not triglycerides.

Plant waxes were compared in forage (Atlas) and grain (\VesternBlackhull) sorghums at different stages in plant groWtll by Cannonand Kummerow (1957). Plant waxes are produced throughout tllegro\vth period by both types of sorghums. A constant level of waxis reached at heading. At maturity, leaves of both varieties containabout 0.30% wax but the stalk of tlle grain sorghum contains 0.60%,while tllat of the forage type contains less than 0.33%. The waxesof the mature leaf, stalk, and grain vary in chemical composition. Cornleaves contain only 1/2 the \vax present in sorghum leaves and cornstalks only :J4 of the wax as those from sorghum.

PHENOLICS

Phenolic compounds contribute flavor and color to sorghum-derivedfeeds and foods. In addition, they may interfere with digestibilityand can be toxic, especially in forage sorghums. The phenolic categoryconsists of many aromatic organic compounds including flavonoids,cyanogenic glycosides, tannins, and lignin. The Sh'llctures of 4 typicalphenolic compounds are shown in Fig. 4.5. The flavonoid group encompasses the antllOcyanidins, anthocyanins, anthocyanogens, flaval1ones,and other related 15-carbon substances. Numerous plant phenolicsillustTated by dhurrin and the flavonoid glycosides, such as cyaninoccur as chemical combinations of an aglycone with various sugars.

146 SORGHUI\f PRODUCTION AND UTILIZATION

FlavonoidsOH

Ho(X,~yH-< )OH"- /CHOH

CHOH

Anthocyanogen [leucofisetinidin)

Cyanogenic GlycosideCH20H C==N

~O-~-H

OH ¢HO ~ IOH "-

OHDhurrin

HO

O·glucoseCyanin [Cyanidin diglucoside]

Lignin PrecursorH2COH

ICHU;;

¥OMeOH

Coniferyl alcohol

OH

FIG. 4.5. STRUCTURES OF SO:\1£ TYPICAL PHENOLIC CO:\fPOUNDS

Grain Phenolics

Pigments.-Varieties of sorghum differ greatly in seed color, rangingfrom white to dark brown, depending on the presence of phenolicpigments. These colors may be transferred to the grits during drymilling and to the starch and gluten during wet milling. Phenolicpigments may cause bitterness and unpalatability of tlle grain and itsproducts. Bird-proof varieties of grain generally have high levelsof phenolics. Grain types with less pigment are being developedfor use in some areas of the United States.

Pigments in several red varieties of sorghum grain were investigatedby Nip and Burns (1968). Orange pigmentation occurred in epicarp,in cross-cell and tube-cell layers of the pericarp, and in seed-tipportions of the grain. Anthocyanin, flavone, and aurone-type compounds were tentatively identified by chromatographic separation andcharacterization, spech'ophotometric measurements, color reactions, andhvdrolvsis products.

, The' red-brown pigments of the seeds of a sweet sorghum wereextracted with methanol and separated on calcium carbonate columns


by Herman et al. (1958). Two anthocyanidins, blood red sanguisorghuidine and ruby red rubisorghuidine, \vere isolated. The pigments are pH-sensitive and soluble in alcohols and acetone, but areinsoluble in water and nonpolar solvents.

A group of colorless flavonoid pigment precursors, termed leucoanthocyanins or anthocyanogens, may be responsible for the developmentof pigments during processing of sorghum grain. These substancesbecome colored in acid solutions. The anthocyanogens apparentlyimpart ash'ingency to foods and beverages. Anthocyanogens weredetected in yellow milo and red kafir sorghums, but not in whitekafir, waxy, and yellow endosperm varieties (Blessin et al. 1963). 'Whenpresent, these compounds are located mainly in the pericarp and aregenerally absent from the endosperm. The anthocyanogens in aqueousextracts of the whole grain were purified on ion-exchange resins andseparated by paper chromatography. Based on spectral absorption,fisentinidin was tentatively identified as one of the reaction productsresulting from treatment of the anthocyanogens with concenh'atedhydrochloric acid at room temperature.

Further investigation indicated the presence of three anthocyanogenlike flavonoids-chromagens I, II, III-in methanol extracts of sorghumpericarp (Yasumatsu et al. 1965). The compounds are polymerizedsubstances similar to those reported in lignin. Upon hydrolysis thethree chromagens yielded a flavanone, probably eridictyol, and ananthocyanidin, pelargonidin.

Tannins.-Sorghum grain varieties with brown seed color are characteristically high in tannin. High tannin levels are thought to affecttheir palatability in feed rations and may be responsible for theirmold resistance. Diets containing sorghum grain high in tannin retardedgro\Vih in poulh-y similar to equivalent levels of tannic acid (Chang andFuller 1964). Tannins were extracted \vith hot water and determinedcolorimetrically with Folin-Denis reagent. Tannin contents in thebrown-seeded sorghums ranged from 1.3 to 2%, compared to a rangeof 0.2 to 0.4% in other common varieties. Barham et al. (1946) foundthat sorghum tannins did not react with some reagents that yieldedcolors with tannic acid. They concluded that sorghum tannins mayconsist of condensed flavonoids, whereas tannic acid is a gallic acidderivative.

Leaf and Stem Phenolics

Cyanogenic Glycosides.-The hydrocyanic acid or prussic acid (HCN)produced in forage sorghum is of special concern to cattle feeders sincecertain levels of HCN are toxic. Although the HCN content of a plant


is often reported, growing sorghums do not contain appreciable freeHCN. Dunstan and Henry (1902) in search of the poisonous substancein sorghum, isolated dhurrin. HCN is liberated from dhurrin by theaction of enzvmes.

An improved isolation method for dhurrin from extracts of sorghumleaves has been reported (Mao et al. 1965) which includes the following steps: (1) Removal of sugars by yeast fermentation, (2) deionization with ion-exchange resins, and (3) cellulose column chromatography. Dhurrin has a melting point of 16:3° to 165°C; [ah 2S _64 0

in water, -650 in ethanol; and pKa 8.9:3. A paper chromatographicstudy of sorghum extracts indicated that dhurrin is the only cyanogenicglycoside present. Physical and chemical data, including ultravioletand infrared spectroscopy and nuclear magnetic resonance, establishedthat dhurrin is p-hydroxY-L-mandelonitrile-,B-D-glucopyranoside (Fig.4.5).

Evidence has been presented by Gander (1966) for the presenceof a phenolic substance not previously reported in sorghum seedlings.The substance is similar to p-hydroxymandelonitrile-j3-glucoside in thatit is derived from D-glucose and L-tyrosine.

The amounts and distribution of dhurrin were determined in germinating etiolated sorghum seedlings (Akazawa et al. 1960). Upon homogenization of the tissues, the cyanogenic glycoside that occurs in theseplants is enzymically hydrolyzed to form equimolar amounts of HCNand p-hydroxybenzaldehyde. The glycoside is localized in aerial shootsof the plant. Seeds of sorghum do not contain the glycoside. HCN insorghum plants at various stages of growth ranges from traces to 335mg per 100 gm. Young plants under 3 weeks have more HCN thando mahlre plants; generally, leaves contain more than stems. Tillerscontain more HCN than the principal stem since they are usuallyless developed. HCN content varies considerably with variety. Favero(1953) reported that nih'ogen fertilizer had 110 influence on HCN content, but Nelson (1953) stated that it increased the HCN level. Braitllwaite (1952) found that the concentration of HCN was greater inyoung plants grown under drought conditions than in those grownunder more favorable moisture conditions (Heinrichs and Anderson1947). Strains can be cut safely only after 50% of their totalprojected growth has taken place. Curing decreases HCN in sorghumforage.

Anthocyal1ins.-'Vheatland sorghum seedlings show' a marked reddenina of stems at earlv stages of growth because of anthocyanin forma-

t:> ' ~ ~ •

tion. Prolonged irradiation at moderately high intensities is requiredfor anthocvanin svnthesis. Anthocvanin svnthesis in seedlings of

,r.; .;" .......,.

COMPOSrI10N OF SORGHU:\I PLANT AND GRAIN 149

sorghum is controlled by two photoreactions (Downs and Siegelman1963). Four-day-old internodes of sorghum grown in complete darkness contained little or no detectable flavonoids, although Cn phenoliccompounds and dhurrin were relatively abundant (Stafford 1965).After light treatment, flavonoids were identified in the nongrowing portions of either intact or excised internodes (Stafford 1965). Two wereanthocyanidins-a red acylated cyanidin-3-glucoside (apigenidin) andorange luteoliniclin. Another was probably the flavone, luteolin. Thesecompounds \vere identified by absorbance spectra and paper chromatography.

The sorghum kernel is encased in glume tissues, which varies considerably in color. Flavonoid pigments were determined in glumetissue from 19 different Nigerian sorghums (Stanton et al. 1959). Paperchromatograms revealed three spots: blue-purple, red, and brown.Black and dark mahogany glumes contained all three types of pigments.The pigments in sorghum glumes are not combined with sugars.

Lignin

Although closely associated with cellulose in fibrous tissues, ligninis a complex phenolic substance. In other species, lignin appears tobe a crosslinked polvmeric material formed from conifervl alcohol(Fig. 4.5) and related substances. Analysis for lignin involves determining insoluble organic matter remaining after hydrolysis of proteinand carbohydrate in tissues extracted with organic solvents.

Crude lignin constitutes approximately 17% of the glumes of Leotisorghum (Edwards and Curtis 1943), and 10 to 20% of the leavesand stems of forage sorghum (Kuniak and Slavik 1960; Bettini andProto 1960; Lengyel and Annus 1960; Sorgato 1949). Lignin contentof forages increases with plant maturity, with values ranging from 3.23to 6.72% for the 1st and 5th cutting, respectively (Achacoso et al.1960). Lignin is higher in stems than leaves at all stages of growth.Application of up to 120 lb nitrogen per acre has no significant influenceon lignin content. Grain sorghums and grass sorghums, such as sudangrass, are highest in lignin content; sweet sorghums are lowest (Table4.5) (Lengyel and Annus 1960). The correlation between lignin andcrude protein was negative, but positive between lignin, crude fiber,and drv matter.,

NONPHENOLIC PIGMENTS

Chlorophylls are responsible for green pigmentation, and carotenoidscause yellow and red colors in natural products. Chlorophylls con-

150 SORGHUM PRODUCTION A?\!) UTILIZATION

tain a nitrogenous porphyrin nucleus, whereas carotenoids are composedsolely of a number of condensed isoprene units. Carotenoid pigmentsinclude two general classes: the carotenes, and the xanthophylls, whichare similar to carotenes but contain hydroxyl groups. The carotenesare important in feeds as vitamin A precursors and as a source of yellowcolor in milk and body fat of cattle. :\Iost xanthophylls, for examplezeaxanthin, do not exhibit vitamin A activity, but do impart thedesirable yellow color to egg yolks and to the skin of broilers.

Carotenoids in Sorghum Grain

At present, corn is the only grain providing significant amounts ofxanthophylls and carotenes in mixed feeds in the United States. However, sorghum varieties found in Nigeria and India with a yellowendosperm contain appreciable carotenoids. Plant breeders in theUnited States have developed yellow endosperm types which containlarger amounts of carotenoids. The grain of common varieties ofsorghum contained about 1.5 ppm total carotenoids, while crossesobtained with yellow endosperm varieties contained as high as 10 ppm(Blessin et aZ. 1962). However, grain of common yellow com hybridshave 21 ppm carotenoids.

Major carotenoids present in extracts of yellow endosperm sorghumcrosses were identified after chromatographic separation. These compounds were zeaxanthin, 2.8 ppm; lutein, 2.2 ppm; and f3-carotene,0.8 ppm. Two other unidentified pigments were also present-xanthophyll I, 1.8 ppm; and xanthophyll II, 0.4 ppm.

A major problem in the development of yellow endosperm varietiesis the rapid loss of carotenoids from sorghum grain in the field (Blessinet aZ. 1962). vVhen exposed to weathering after pollination, sorghumretained only 50% of the carotenoids present in protected seed heads.Carotenes and xanthophylls decreased continuously with no preferentialloss of individual carotenoids. Colored pericarps did not inhibit lossof carotenoids.

The inheritance of f3-carotene content was studied in the grain ofeight sorghum crosses and of their parents (Worzella et aZ. 1965).f3-Carotene in the grain of the parents ranged from 0.22 to 3.23 mgper kg. Although concentration in the F 2 segregates generally fellbetween the parents, there was a preponderance of segregates with af3-carotene content lower than the midparent value. Positive correlation coefficients were obtained between endosperm color and f3-carotenecontent in the F2.

COMPOSITION OF SORGHUM PLA.I."T AND GRAIN 151

•

,

Nonphenolic Pigments in Leaf and Stem

Various pigments account for 9% of the total solids extracted fromsorghum leaf and stem with acetone and hexane (Burnett et al. 1958).On a dry weight basis two types of chlorophyll, a and b, were themajor pigment components, 6,200 and 1,800 ppm. f3-Carotene (100ppm) and other carotenoids (40 ppm) were also present.

VITAMINS

The importance of vitamins in grain and forage to animal nuh'itionis well established. Vitamins generally are classed according to theirsolubility. Water-soluble vitamins include niacin, thiamine, folacin,riboflavin, B12, and C. Fat-soluble vitamins include tocopherol (E)and the carotenes, which are vitamin A precursors.

Grain Vitamins

Data on sorghum grain vitamin composition averaged from a numberof sources are given in Table 4.11 (Hubbard et al. 1950; Tanner et al.1947; Naik and Abhyankar 1955). Compared to corn, sorghum graincontains approximately the same quantities of riboflavin, and pyridoxine,but more pantothenic acid, nicotinic acid, and biotin (Tanner et al.1947). Grain sorghum compares favorably with wheat and rice withregard to levels of thiamine and niacin, but it is poorer in riboflavin(Naik and Abhyankar 1955).

The average dish'ibution of vitamins in hand-dissected fractions from5 varieties of sorghum (Table 4.11) was determined by Hubbard et al.(1950) . The germ has 2 to 5 times the quantity of vitamins presentin endosperm and bran. The germ and bran contain about equalamounts of riboflavin, whereas the bran and endosperm contain aboutthe same concentration of niacin, pantothenic acid, and pyridoxine.The amount of individual vitamins varies considerably among varieties.

The development of sorghum varieties with high-niacin content ispossible (Tanner et al. 1949). Niacin in grain from Westland plants(43.0 to 49.1 f-tg niacin per gm) by Cody cross (66.9 to 72.9 f-tg pergm) was determined. Some F3 generations had as much as 124 f-tgof niacin per gram.

The biological availability of niacin in sorghum is important sincepellagra in humans has been associated with sorghum diets. Niacinin sorghum grain estimated by chemical and microbiological methodsbefore and after hydrolysis by acid or alkali was not significantly dif-

Arter HubhHl'd t!t al. (HHiO).

TAIlLB 4'.11AVI,mAGB VITAMIN COMI'ORI'l'ION OF WllOI,B ROIlGIIUM GHAIN AND I'HAc'rIONS

Vitamin Content, fJ.g/Gm

Fraction

Wholc grainEndospcrmGcrulBran

Niacin

45.84}1.780.744.0

PantothcnicAcid

lOA8.7

82.210.0

Ribollnvin

1. }lo.n8.n'1.0

Biotin

0.200.11o.m0.85

Pyridoxinc

4.7,1,.07.'24,.4

'l'hialllinc

8.3

AscorbicAcid (C)

21. 0

Choline

'120.0

I-'CJ(1:0

UJo

~q1,;7M

;ggqn::1oZ:>zt;j

q::1~:>-::1oz

COMPOSITION OF SORGHUM PLANT A.,-';1) GRAL'\' 153

•

ferent (Belavady and Gopalan 1966). Therefore, pellagra cannot beex-plained on the basis of a primary niacin deficiency due to an unavailable form in sorghum. These results are in disagreement withfindings on the availability of niacin in milo for s\V'ine (Luce et al.1967). The addition of crystalline niacin improved weight gains ofpigs fed rations containing sorghum grain as the primary source ofenergy. Total niacin of the grain sorghum ration equalled or exceededthe recommended level. These experiments indicate that niacin insorghum grain is largely unavailable to swine.

Leaf and Stem Vitamins

Carotene content of forage material from sorghum and sudangrasshas been reported as 6.0 and 2.0 p.g per gm (Acha and Dora 1955).Tocopherol content in leaves decreased from 333 p.g per gm after 1week of growth to 150 after 5 weeks and then increased to 243 p.gper gm of dry matter after 11 \veeks (Ramanujan and Anantakrishnan1958). The leaf-to-stem ratios were 2.9, 1.7, and 6.1 at 1, 5, and 11weeks respectively. At corresponding times carotene values in leaveswere 945, 592, and 617 p.g per gm. The apex of the leaf containedmore tocopherol and carotene than the base or lamina. Tocopherolwas greater in plants grO\vn in the winter than in plants grown in thesummer. Shade drying of the plants did not preserve more tocopherolor carotene than sun drying.

OTHER ORGAl'iIC SUBSTANCES m SORGHUM

Acids

Titratable acidity in sorghum stem juices normally increases duringthe harvest season-often doubling or h'ipling before the season ends(vVebster et al. 1954). This increase in acid compounds has beencited as a reason for poor quality syrup late in the season. The majororganic acid of sorghum juice is aconitic acid, 12 mg per ml, \vhichmay settle out as the calcium salt during concentration of the neutralized juice. t-.Jader and Webster (1954) using partition chromatography on silica gel columns, found that tartaric, malic, and citricacids were present in juices at 11, 5, and 2 mg per ml, respectively.Oxalic, fumaric, and acetic were in a lower concenh·ation. They foundlarge differences among varieties.

Disease resistance and detrimental effects of plant residues on cropgrowth have been ath'ibuted to phenolic acids in sorghum. Guenzi andMcCalla (1966) quantitatively estimated five phenolic acids, ferulic,

154 SORGHUM PRODUCTION A~Tl) UTILIZATION

p-coumaric, syringic, vanillic, and p-hydroxybenzoic, in sorghum plantresidues. In alkaline and acid hydrolyzates, p-coumaric acid waspresent in the largest amount, 1.5%. Almost all the phenolic acidsoccur in the plant combined with sugars.

Phytic acids, the phosphoric acid esters of inositol, are widely distributed in plants, especially in seeds. Phytic acid is capable of forming complexes with certain ions. It has been implicated as impairingthe calcium and zinc metabolism of animals. Phytic acid is determinedby phosphorus analysis of the insoluble iron salt. Wang et al. (1959)established that the phytic acid in sorghum grain occurs primarily as theinositol hexaphosphate. These workers determined the phytic acid invarious parts of several varieties of sorghum grain. Phytate phosphorusranged from 0.20 to 0.37% in the whole grain. The germ was highestin phytate ranging from 0.54 to 1.91%; bran, from 0.19 to 0.49%; andgrits, from 0.03 to 0.07%. Becker (1950) found that of various grainsanalyzed, sorghum had the highest percentage of its phosphorus presentin phytic acid, 75%. Johri and Kehar (1962) report that green sorghumfodder contains 149.0 mg phytic acid phosphorus per 100 gm dry matter, which amount accounts for 33% of its total phosphorus. In sorghumstraws, 65.5 mg of phytic acid phosphorus occurs per 100 gm drymatter. Sudangrass contains 292 mg phytic acid per 100 gm dry matter.

About 2% of the nitrogen of sorghum grain is contained in lowmolecular-weight compounds. Reindel and Scheublein (1959), using2-dimensional paper chromatography, identified 21 different amino acidsin extracts of sorghum. Compounds included were ornithine, glutamine,asparagine, y-aminobutyric acid, and a-aminobutyric acid, as well asother amino acids.

Growth Substances

Like corn and some other grains, sorghum grain appears to be asource of auxin-like growth substances related to indoleacetic acid.Netien (1965A) found that the growth of tissue cultures of artichokeparenchyma was proportional to the amount of sorghum extract addedto the tissue culture. Auxin activity was contained mainly in basicand neutral fractions of grain extracts.

Gibberellins serve to stimulate germination and enzyme development in grains, as well as to promote cell elongation. Extracts ofimmature sorghum grain were concentrated and applied to germinating pea plants (Netien 1965B). The response in growth indicatedthat gibberellin-like material was present at a concentration of 12.5 fLgper kg grain.

C01>IPOSITION OF SORGHUM PLANT AND GRAIN 155

,

Nucleic Acids

The importance of deoxyribonucleic acid (DNA) as the agent governing the genetic character of plants and of ribonucleic acid (RNA),which determines the synthesis of proteins, has prompted their studyin sorghum. The nucleic acids are large polymers consisting of chainsof nucleotides whose sequences serve as a code for the arrangementsof amino acids in proteins. Nilson and Pauli (1964) investigated thelevels of RNA and DNA during root growth of sorghum seedlings. Thecontent of both nucleic acids was higher in the roots of 2 hybridsorghums, RS 610 and RS 501, than in 2 milo varieties. RNA and DNAconcentration was greatest in root parts vlhere cell division was continuing. Nirula et al. (1961) tried to correlate the size of chromosomesin sorghum cells with the nuclear DNA content. In sorghums differingin chromosome number, size, and stainability, the DNA content per unitlength differed. They attributed this difference to variations in observedheterochromatin in the chromosomes of the different sorghums.

MINERALS

Levels of minerals in sorghum grain and plant parts depend ona number of variables, such as variety, soil conditions, temperature,rainfall, and fertilizer.

Grain Minerals

Although numerous studies have been made of the composition ofminerals in sorghum grain, the most comprehensive data are reportedby Pinta and Busson (1963). Phosphorus, magnesium, potassium, andsilicon are the major minerals in sorghum grain with lesser amountsof calcium and sodium also present (Table 4.12). Data on othermineral elements ranging in concentration from less than 0.5 to 150 ppmare also given. About 20% of the total calcium and 13% of the totalphosphorus are in the fibrous seed coat (Kurien et al. 1960). From40 to 75% of the phosphorus is present as phytate phosphorus (Naikand Abhyankar 1955). Variations in calcium and phosphorus amongsome varieties and hybrids are given in Table 4.3 (Bressani and Rios1962).

Leaf and Stem Minerals

Analyses for minerals in sorghum roughages have been compiled(National Academy of Sciences 1958). Average data in Table 4.13

156 SORGHUM PRODUCTION A"1) UTILIZATION

TABLE 4.1~

C01IPOSITION" OF MIN"ERALS IN" SORGH1DI GRAIN"

Element

SiNaKCal\lgPTotal ash

AlBBaCrCuFeLiMIlMoNiPhRbSIlSrTiVZIlAgBeBiCoGaGe

Range

Conccntration, 0/00.1-0.3

0.01-0.0S!0.35-0.5S!0.02-0.030.13-0.230.43-0.63

1. 9-S!. 5

Concentration, Ppm5-691-3

0.S!-20.~-1

3-1038-150o 0_,)

16-30~-8

1-40.~-2

1-30.04-1. 50.1-30.~-2

16-75

Average

0.200.020.400.020.180.492.~0

17.61.30.80.55.4

670.7

2141.71.11.S!o 51.81.00.1

370.050.50.50.50.10.1

After Pinta and Busson (1963).

TABLE 4.13AYERAGE MIN"ERAL C01IPOSITION" OF DRY SORGHUM AN"D SUDAN"GRASS ROUGHAGES

Mineral, %

CalciumPhosphorusCopper, l\lg/lbPotassiumMagnesiumIronManganese, Mg/lbSulfurSodiumChlorineCobalt, l\Jg/lb

National Academy of Sciences (1958).

Sorghum Hay

0.400.173.91.40.320.005

5£.5

0.020.63

Sudangrass Hay

0.560.31

16.71.50.40.0174~.3

0.060.02

0.06

COMPOSITION OF SORGHUM PLANT AND GR.AIN 157

indicate that potassium, the major mineral, makes up from 1.4 to 2.1%total dry matter. In general, various dry and green sorghum roughageshave similar mineral compositions. Ho\vever, limited data indicate thatsudangrass contains more copper than does sorghum fodder.

Silica, calcium, and iron were determined in various parts of eightdifferent hybrid sorghum plants (Lanning and Garabedian 1963).Roots contained 5.0% silica as compared to 4.0 and 2.9% in the sheathand leaves, respectively. Iron content (0.10%) of sorghum roots was4 times higher than in leaves and sheath, both of which had nearlythe same amount of iron. Calcium in the sorghum sheath (0.46% ) was2.5 times that of the leaves and 6 times that of the roots.

ENZYMES OF SORGHUM

To catalyze the chemical reactions necessary for its metabolism, thesorghum plant possesses many enzymes. Enzymes are generally salinesoluble proteins. For their activity they may require cofactors, suchas metal ions or various low-molecular-weight organic substances.

Amylases

The most extensively studied enzymes of sorghum grain are thosethat degrade starch. Two kinds of amylases occur in plants. Thea-amylase cleaves a-1,4 linkages at random. The j3-amylases promoterapid hydrolysis of outer chains by breaking off 2 sugar units at a time(terminal maltose units), but they cannot hydrolyze or bypass a-1,6linkages and, therefore, leave residual limit dextrans. Kneen (1944)found no j3-amylases in ungerminated sorghum grain, but found smallamounts of a-amylase as both free and bound enzyme. The bounda-amylase required protease activity to release it into solution. Sorghumgrain had less a-amylase activity than oats, com, or barley in theungerminated state.

\Vhen allow"ed to germinate, sorghum grain exhibits a large increasein a-amylase activity (Kneen 1944). Germinated or malted sorghumgrain serves as a source of enzymes for saccharification of starch beforebeverage fermentations as in preparation of native African beers. Thesorghum a-amylase is stable to heating to 70°C. Its pH optimum from20° to 40°C is 4.6 (Kneen 1945). It requires calcium ions for itsactivity. The a-amylase has been isolated from sorghum malts andpurified by Dube and Nordin (1961) and by Botes et al. (1967A).Its molecular weight of 50,000 is similar to that of other a-amylases, andit contains 3 to 4 gm atoms of calcium per mole and 2% bound carbo-

158 SORGHUM PRODUCTION ANi) UTILIZATION

hydrate. Paper chromatography of a-amylase digests of starch revealsthat it forms mainly chains of 6 and 7 glucose units when the starchiodine color no longer appears, but as digestion continues, smalleroligosaccharides and maltose prevail (Dube and Nordin 1962).

In sorghum malt ,B-amylase accounts for only about 18% of the totalamylase activity. NovelIie (1960) concentrated it in malt extracts byammonium sulfate fractionation. Ethanol fractionation and ion exchange chromatography were used by Botes et al. (1967B) to purifythe enzyme further. The purified ,B-amylase has a pH optimum at 5.3to 5.4. Only 55% of starch is converted to sugars by this enzyme.

Dyer and NovelIie (1966) studied the distribution and activity ofa- and ,B-amylases in germinating sorghum grain. Initially a-amylaseis located mainly in the embryo, but as malting continues, both a and,B activity exist in the endosperm as well as in the germ. The optimumdevelopment of the malt requires high moisture and a temperature of25° to 30°C; maximum diastatic activity occurs at 6 to 7 days (Novellie1962A). In addition to varietal differences of sorghums in malt quality,differences result from location and season of gro\vth and storage conditions of grain (Novellie 1962B).

:Many substances have been reported in grains that serve to inhibitamylase activities. Miller and Kneen (1941) isolated a high-molecularweight organic acid from Leoti sorghum grain that reversibly inhibitedbarley malt amylase. The substance was not in most varieties tested andwas concentrated mainly in the bran and germ.

Oxidative Enzymes

Enzymes have been investigated in sorghum grain and malt thatcatalyze oxidation of various substances. Peroxidase is an iron-porphyrinenzyme that promotes oxidation of substrates by hydrogen peroxide.Sorghum grain has less activity than sorghum after 7 days germination.Germinated sorghum exhibits much less activity than barley malt orgrain (Reindel and Scheublein 1959). After 6 days germination, peroxidase activity increased rapidly in the sorghum embryo, according toGopalachari (1963), with a smaller increase in the endosperm. Polyphenol oxidase, a copper-containing enzyme that oxidizes phenolic compounds, is absent in the mature grain but appears upon germination.

Hydrolases of Cyanogenic Glycosides

The importance of the cyanogenic glycoside, dhurrin, in youngsorghum plants has stimulated studies on its enzymic synthesis anddegradation. Homogenization of the plant results in rapid hydrolysis

COMPOSITION OF SORGHUM PLANT A1'<1) GRAIN 159

of the compound to yield HCN. Dunstan and Henry (1902) demonstrated an enzyme that hydrolyzes the glycosidic linkage between glucose and p-hydroxybenzaldehyde cyanohydrin. J\Iao and Anderson(1967) have reported the isolation of two ,B-n-glucopyranosidases insorghum vegetative tissues and seeds, but only one hydrolyzes dhurrin.The seeds have a higher concentTation of enzyme than the plant. Anenzyme that next decomposes the cyanohydrin of p-hydroxybenzaldehydefrom etiolated seedlings of sorghum has been isolated also, purified,and designated hydroxynih'ilyase (Seely et al. 1966). This enzyme hasa pH optimum of 5 and is specific only for the L-isomer. The endospermis inactive; greatest activity is in the developing epicotyl with lesseractivitv in the roots.

.'

Sorghum seedlings have been widely used as enzyme sources instudies of many metabolic processes in plants, including photosynthesisand starch synthesis.

With the gro\'ling production of sorghum for forage and grain increased research is needed on its composition and metabolic processes.

ACKNOWLEDGMENTS

The authors wish to thank numerous investigators for permIssIOnto cite their data in the text. To Mr. T. F. Clark of Northern RegionalLaboratory vve are indebted for information on pulp production fromsorghum. \Ve express appreciation to Professor EmerihiS J. E. \Vebsterof Oklahoma State University for helpful suggestions. Also we aregrateful to Miss Virginia M. Thomas for her assistance in editing themanuscript.

BIBLIOGRAPHY

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Joseph S. Wall Composition of Sorghum Plant Charles W ... · Composition of Sorghum Plant and Grain1 INTRODUCTION As cultivation of sorghum became widespread, different varieties

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